JP-A-10-104103 discloses an example of the tire-state obtaining apparatus described above. In this tire-state obtaining apparatus, each of the wheel-side devices includes (a) a tire-state detecting device operable to detect the state of the corresponding tire, and (b) a transmitter device operable to transmit a series of tire information including tire-state information indicative of the tire state detected by the tire-state detecting device, while the body-side device includes (c) a receiver device including a plurality of antennas disposed near the respective wheels, and (d) a wheel-position-data obtaining device operable to obtain wheel-position data indicative of the position of each wheel whose tire information has been received by the receiver device, such that the wheel-position data are obtained on the basis of intensities of reception of the tire information as received by the receiver device.